1. Field of the Invention
The present invention relates generally to rotating machines such as electric motors and generators and, more particularly, to electric motors and generators having a current-carrying stator with an induced current in a rotating inner rotor with coolant passing through the current carrying portion of the rotor.
2. Prior Art
There have been many proposals intended to improve the operation of transducers for electrical power/mechanical power conversion (motors or generators). However, there are still areas where the use of electric motors remains impractical, for example for use as the main drive of a vehicle such as a car. Current electric motors are generally too large, heavy, and produce too little power (especially at high speed) for commercial use in a vehicle such as a car.
One problem associated with electrical machines, such as electric motors, is that it is necessary to cool them because they generate heat which reduces their efficiency. The need for optimization in cooling is even more important as increases in performance demands smaller packages. At present such machines may be cooled by blowing air through or over them. For heavy duty applications it is known to spray oil onto the rotor and stator assemblies and into the gap between them using a high pressure pump. A scavenger pump may also be provided to collect the sprayed oil for re-cycling.
A common configuration for such motors is to have an inner rotor mounted on a straight shaft supported by bearings on the ends. The bearings are mounted in end covers that support and locate the rotor in the center of a current-carrying stator. The rotor contains multiple current-carrying bars which run length wise parallel to the shaft and are located near the outer circumference of the rotor. Heat is produced in the rotor when the current in the stator excites the bars. Heat dissipation limits the design of the rotor. Another method used to dissipate heat is to pass oil coolant through a hollow rotor shaft, referred to as back iron cooling. Heat generated in the rotor conductor bars is dissipated into the core of the rotor, then into the rotor shaft and then into the oil coolant flowing through the shaft and exits the rotating machine to a heat exchanger. Although this cooling method has its advantages, such as simplicity in design, it is desirable to increase the amount of heat conduction away from the rotor bars of the motor and to concentrate the cooling at the source of the heat, namely, the rotor bars.
Therefore it is an object of the present invention to provide a rotating machine with cooled hollow rotor bars which provides an increased amount of cooling than is provided by prior art methods for cooling rotating machines.
In order to increase heat conduction away from a plurality of rotor bars of a rotating machine, oil coolant is passed through the rotor bars. Oil coolant is supplied to and removed from the rotor bars via left and right end plates. The end plates are preferably round disks located on either end of the rotor. The end plates have conduits therein to allow the flow of coolant oil in the rotor bars on one end and out on the other end. Holes located in a rotating hollow shaft under each end plate and communicating with the conduits of the end plates allow oil coolant to flow in and out of the hollow shaft. A restriction located near the middle of the hollow shaft and between the end plates provides a pressure differential to divert at least a portion of the coolant oil to flow through the rotor bars.
In summary, there is provided an improved rotating machine. The improved rotating machine comprises: a rotating shaft: a plurality of conductive rotor bars spaced from the rotating shaft and fixed thereto through at least one intermediate member, at least one of the plurality of conductive rotor bars having at least one first internal conduit; and circulation means for establishing a coolant circulation through the first internal conduit.
In a preferred implementation of the rotating machine, the rotating shaft has a first wall defining a second internal conduit extending from an inlet end to an outlet end thereof. The rotating shaft further has first and second coolant holes in the wall and communicating with the second internal conduit, wherein the coolant is circulated through the first internal conduit from the second internal conduit by way of the first and second coolant holes. Furthermore, each of the plurality of conductive rotor bars have a first and second end where the at least one first internal conduit extends from the first to second end. A first end plate has a first bore in which the rotating shaft is sealingly fixed in proximity to the first coolant hole. The first end plate further has means for sealingly fixing the first end of each conductive rotor bar having the at least one first internal conduit thereto and a third internal conduit for each of the plurality of conductive rotor bars having the at least one first internal conduit for providing communication between the first coolant hole and the first end of the first internal conduit. A second end plate has a second bore in which the rotating shaft is sealingly fixed in proximity to the second cooling hole. The second end plate further has means for sealingly fixing the second end of each conductive rotor bar having the at least one first internal conduit thereto and a fourth internal conduit for each of the plurality of conductive rotor bars having the at least one first internal conduit for providing communication between the second coolant hole and the second end of the first internal conduit. Thus, the circulation of coolant is established through the first, second, third, and fourth internal conduits for each conductive rotor bar having the at least one second internal conduit.
The circulation means comprises either a full restriction plug disposed in the second internal conduit between the first and second coolant holes thereby diverting all of the fluid flow through the first, third, and fourth internal conduits for each conductive rotor bar having the at least one first internal conduit. Alternatively, the circulation means comprises a partial restriction plug disposed in the second internal conduit between the first and second coolant holes. Thus, in the alternative version, which is also the preferred implementation, a portion of the fluid flow is diverted through the first, third, and fourth internal conduits for each conductive rotor bar having the at least one first internal conduit and the remaining portion of the fluid flow continues through the second internal conduit of the rotating shaft.
In yet another preferred implementation of the rotating machine of the present invention, each of the plurality of conductive rotor bars have the at least one first internal conduit. In yet a more preferred implementation of the rotating machine of the present invention, the at least one first internal conduit comprises two first internal conduits, each extending from the first to second end of the conductive rotor bars.
In yet another preferred implementation of the rotating machine of the present invention, each of the first and second end plates further has an access bore disposed in a fluid path of the third and fourth internal conduits, respectively, for facilitating the fabrication of the third and fourth internal conduits, and wherein the first and second end plates each further comprise a cover plate sealingly covering its respective access bore.
In yet still another preferred implementation of the rotating machine of the present invention, the rotating machine further comprises: a circulation conduit connecting the inlet end of the rotating shaft to the outlet end of the rotating shaft; a pump disposed in a fluid path of the circulation conduit for establishing a fluid flow into the inlet end, through the first, second, third, and fourth internal conduits for each conductive rotor bar having the at least one first internal conduit, and out the outlet end; and a heat exchanger disposed in the fluid path of the circulation conduit for removing heat from the fluid flowing therein.
Also provided is a method for assembling the rotating machine of the present invention. The method comprises the steps of: assembling the plurality of conductive rotor bars to the at least one intermediate member and the first end of each conductive rotor bar having the at least one internal conduit to the first end plate; heating the top region of a molten salts bath such that the top region is maintained at a normal brazing temperature; only immersing the first end plate and the first ends of the plurality of conductive rotor bars into the top region of the molten salts bath; salts brazing the first end of each conductive rotor bar having the at least one internal conduit to the first end plate; either before or after the salts brazing of the first end of each conductive rotor bar having the at least one internal conduit, assembling the second end plate to the second end of each rotor bar having the at least one internal conduit to the second end plate; only immersing the second end plate and the second ends of the plurality of rotor bars into the top region of the molten salts bath; and salts brazing the second end of each conductive rotor bar having the at least one internal conduit to the second end plate.